Lubricating oil composition

ABSTRACT

A lubricating oil composition which may contain a zinc dialkyl dithiophosphate, and whose color deterioration over time is alleviated. Such a lubricating oil composition may contain: a base oil (A); a zinc dialkyl dithiophosphate (B); and a sodium-based detergent (C). In such a lubricating oil composition, a content of zinc atoms may be 100 ppm by mass to 2,000 ppm by mass based on a total amount of the lubricating oil composition, and a content of sodium atoms may be 5 ppm by mass to 1,000 ppm by mass based on the total amount of the lubricating oil composition.

TECHNICAL FIELD

The present invention relates to a lubricating oil composition.

BACKGROUND ART

Zinc dialkyl dithiophosphates are widely used in lubricating oil compositions from a viewpoint of imparting an anti-oxidation ability, an anti-wear ability, and the like.

As described above, the zinc dialkyl dithiophosphate is excellent in that the zinc dialkyl dithiophosphate can impart the anti-oxidation ability, the anti-wear ability, and the like to a lubricating oil composition, and also has the other aspect that thermal oxidation and the like is likely to cause sludge generation, and therefore, various methods of reducing sludge derived from the zinc dialkyl dithiophosphate are adopted.

For example, PTL 1 discloses that an overbased metal salicylate is blended in an industrial hydraulic oil composition in order to reduce the sludge derived from the zinc dialkyl dithiophosphate. PTL 1 also discloses that a metal component constituting the overbased metal salicylate is an alkaline earth metal such as calcium and magnesium, and preferably calcium.

CITATION LIST Patent Literature

-   PTL 1: JP-A-2016-089043

SUMMARY OF INVENTION Technical Problem

However, the lubricating oil composition tends to gradually deteriorate with time of use and a color tends to deteriorate (the color becomes deep). Therefore, in order to easily grasp a deterioration state of the lubricating oil composition, a deterioration determination method using a color change of the lubricating oil composition is widely used in management of machines, facilities, and the like using the lubricating oil composition.

However, while the color deterioration of the lubricating oil composition blended with the zinc dialkyl dithiophosphate tends to occur, performance of the lubricating oil composition may be maintained even after the color deterioration occurs. Therefore, there is a problem that the deterioration state cannot be unconditionally determined only by the color change.

In the management of machines, facilities, and the like using the lubricating oil composition, a state of contamination, a state of generation of precipitates, and the like are often visually checked. However, when the color deterioration of the lubricating oil composition occurs at an early stage, visibility of the state of contamination of the lubricating oil composition, the state of generation of precipitates, and the like deteriorates, and the state of contamination, the state of generation of precipitates, and the like cannot be visually recognized. As a result, there is a risk that the machines, the facilities, and the like may stop.

Therefore, the present inventors have considered to make the color deterioration over time of the lubricating oil composition blended with the zinc dialkyl dithiophosphate to be alleviated. As a result, it is considered that a period during which the state of contamination of the lubricating oil composition, the state of generation of precipitates, and the like can be appropriately visually observed can be extended, and the risk of stopping the machines, the facilities, and the like due to the state of contamination, the state of generation of precipitates, and the like not being visually recognized can be reduced. In addition, it can be said that alleviating the color deterioration of the lubricating oil composition prevents at least oxidative deterioration of the lubricating oil composition, and thus it can be said that this is a desirable countermeasure for the lubricating oil composition.

An object of the present invention is to provide a lubricating oil composition which contains a zinc dialkyl dithiophosphate, and whose color deterioration over time is alleviated.

Solution to Problem

The present inventors have conducted intensive studies to solve the above problems, and have completed the following inventions.

That is, the present invention relates to the following [1].

[1] A lubricating oil composition containing:

a base oil (A);

a zinc dialkyl dithiophosphate (B); and

a sodium-based detergent (C),

wherein a content of zinc atoms is 100 ppm by mass to 2,000 ppm by mass based on a total amount of the lubricating oil composition, and

a content of sodium atoms is 5 ppm by mass to 1,000 ppm by mass based on the total amount of the lubricating oil composition.

Advantageous Effects of Invention

According to the present invention, it is possible to provide a lubricating oil composition which contains a zinc dialkyl dithiophosphate, and whose color deterioration over time is alleviated.

DESCRIPTION OF EMBODIMENTS

In this specification, regarding a preferred numerical range (for example, a range of a content or the like), a lower limit value and an upper limit value that are expressed in stages can be combined each independently. For example, based on an expression of “preferably 10 to 90, and more preferably 30 to 60”, by combining the “preferred lower limit value (10)” and the “more preferred upper limit value (60)”, a suitable range can also be conceived as “10 to 60”.

In addition, in this specification, numerical values in Examples are numerical values that can be used as an upper limit value or a lower limit value.

In addition, in this specification, a numerical range described as “A to B” means “A or more and B or less” unless otherwise specified.

Embodiment of Lubricating Oil Composition of Present Invention

A lubricating oil composition of the present invention is a lubricating oil composition containing: a base oil (A); a zinc dialkyl dithiophosphate (B); and a sodium-based detergent (C), in which a content of zinc atoms is 100 ppm by mass to 2,000 ppm by mass based on a total amount of the lubricating oil composition, and a content of sodium atoms is 5 ppm by mass to 1,000 ppm by mass based on the total amount of the lubricating oil composition.

The present inventors conducted intensive studies on a lubricating oil composition containing a zinc dialkyl dithiophosphate (hereinafter, also referred to as “ZnDTP”) in order to alleviate the color deterioration over time. As a result, it has been found that a lubricating oil composition in which a ZnDTP and a sodium-based detergent are used in combination and the zinc atom content and the sodium atom content are respectively adjusted to specific ranges can make the color deterioration over time to be alleviated.

According to the studies conducted by the present inventors, it was found that when the ZnDTP and the sodium-based detergent were blended separately into the lubricating oil composition without being combined with each other, the color deterioration over time was likely to occur at an early stage. In particular, when the sodium-based detergent was blended alone, the color deterioration over time was remarkable.

However, it was found that when the ZnDTP and the sodium-based detergent were combined and blended in the lubricating oil composition, unexpectedly, the color deterioration over time became extremely alleviated.

Although a detailed mechanism of this phenomenon is not clear, it is considered that at least the color deterioration of the lubricating oil composition due to an influence of the ZnDTP is prevented by the sodium-based detergent, and the color deterioration due to an influence of the sodium-based detergent is prevented by the ZnDTP. In other words, it is presumed that an interaction between the ZnDTP and the sodium-based detergent can prevent the color deterioration that occurs at the early stage when the ZnDTP and the sodium-based detergent are separately blended in the lubricating oil composition, and effects of the present invention are exhibited.

The effects of the present invention are effects that are not exhibited when the sodium-based detergent is replaced with a calcium-based detergent or a magnesium-based detergent.

In the following description, the “base oil (A)”, the “ZnDTP (B)”, and the “sodium-based detergent (C)” are also referred to as a “component (A)”, a “component (B)”, and a “component (C)”, respectively.

The lubricating oil composition of the one embodiment of the present invention may contain only the “component (A)”, the “component (B)”, and the “component (C)”, and may also contain components other than the “component (A)”, the “component (B)”, and the “component (C)” as long as the effects of the present invention are not impaired.

In the one embodiment of the present invention, from a viewpoint of being easier to exhibit the effects of the present invention, a total content of the component (A), the component (B), and the component (C) is preferably 70.0% by mass to 100% by mass, more preferably 80.0% by mass to 100% by mass, still more preferably 90.0% by mass to 100% by mass, and yet still more preferably 95.0% by mass to 100% by mass, based on a total amount of the lubricating oil composition.

Hereinafter, the base oil (A), the ZnDTP (B), the sodium-based detergent (C), and other additives will be described in detail.

<Base Oil (A)>

The lubricating oil composition of the present invention contains the base oil (A).

As the base oil (A), one or more selected from mineral oils and synthetic oils used in related art as base oils for lubricating oils can be used without particular limitation.

Examples of the mineral oils include atmospheric residual oils obtained by subjecting a crude oil, such as a paraffinic crude oil, an intermediate base crude oil, and a naphthenic crude oil, to atmospheric distillation; distillate oils obtained by subjecting such an atmospheric residual oil to vacuum distillation; and mineral oils obtained by subjecting the distillate oils to at least one refining treatment, such as solvent deasphalting, solvent extraction, hydrogenation, solvent dewaxing, catalytic dewaxing, and hydrorefining.

Examples of the synthetic oils include: poly-α-olefins such as an α-olefin homopolymer and an α-olefin copolymer (for example, an α-olefin copolymer having 8 to 14 carbon atoms, such as an ethylene-α-olefin copolymer); isoparaffins; various esters such as polyol esters and dibasic acid esters; various ethers such as polyphenyl ethers; polyalkylene glycols; alkyl benzenes; alkyl naphthalenes; and gas-to-liquids (GTL) base oils obtained by isomerizing a wax (GTL wax) produced from a natural gas by a Fischer-Tropsch method or the like.

As the base oil (A), a mineral oil may be used alone or a plurality of mineral oils may be used in combination, or a synthetic oil may be used alone or a plurality of synthetic oils may be used in combination. In addition, one or more mineral oils and one or more synthetic oils may be used in combination.

From a viewpoint of further improving oxidation stability of the lubricating oil composition, the base oil (A) is preferably one or more selected from base oils classified into Groups II, III, and IV in the base oil category of the American Petroleum Institute (API), and more preferably one or more selected from the base oils classified into Groups II and III.

Kinematic viscosity at 40° C. of the base oil (A) (hereinafter also referred to as “kinematic viscosity at 40° C.”) is preferably 8.00 mm²/s or more, more preferably 10.0 mm²/s or more, and still more preferably 15.0 mm²/s or more. In addition, the kinematic viscosity at 40° C. is preferably 150 mm²/s or less, more preferably 120 mm²/s or less, and still more preferably 100 mm²/s or less. Upper limit values and lower limit values of these numerical ranges can be freely combined as desired. Specifically, the kinematic viscosity at 40° C. is preferably 8.00 mm²/s to 150 mm²/s, more preferably 10.0 mm²/s to 120 mm²/s, and still more preferably 15.0 mm²/s to 100 mm²/s.

When the kinematic viscosity at 40° C. of the base oil (A) is 8.00 mm²/s or more, a lubricating oil composition having a high flash point and excellent lubricating performance can be easily obtained.

In addition, when the kinematic viscosity at 40° C. of the base oil (A) is 150 mm²/s or less, viscosity resistance at a low temperature is not excessively large, so that operations of a machine are easily improved.

A viscosity index of the base oil (A) is preferably 80 or more, more preferably 90 or more, and still more preferably 100 or more. When the viscosity index of the base oil (A) is in the above range, viscosity changes caused by temperature changes can be reduced, an oil film can be easily formed under high temperature, and thus wear resistance is easily improved.

When the base oil (A) is a mixed base oil containing two or more types of base oils, the kinematic viscosity at 40° C. and the viscosity index of the mixed base oil are preferably within the above ranges.

In this specification, the kinematic viscosity at 40° C. and the viscosity index mean values measured or calculated in conformity with JIS K2283:2000.

In the lubricating oil composition of the one aspect of the present invention, from the viewpoint of being easier to exhibit the effects of the present invention, a content of the base oil (A) is preferably 80.0% by mass or more, more preferably 85.0% by mass or more, and still more preferably 90.0% by mass or more based on the total amount of the lubricating oil composition. In addition, the content of the base oil (A) is preferably 99.84% by mass or less, more preferably 99.80% by mass or less, and still more preferably 99.50% by mass or less. Upper limit values and lower limit values of these numerical ranges can be freely combined as desired. Specifically, the content of the base oil (A) is preferably 80.0% by mass to 99.84% by mass, more preferably 85.0% by mass to 99.80% by mass, and still more preferably 90.0% by mass to 99.50% by mass.

<ZnDTP (B)>

The lubricating oil composition of the present invention contains the ZnDTP (B).

When the lubricating oil composition contains the ZnDTP (B), the lubricating oil composition is imparted with an anti-oxidation ability, an anti-wear ability, and the like.

When the lubricating oil composition does not contain the ZnDTP (B), the effects of the present invention by combining the ZnDTP (B) and the sodium-based detergent (C) are not exhibited.

Preferred examples of the ZnDTP (B) used in the lubricating oil composition of the one aspect of the present invention include those represented by the following general formula (b1).

In the above general formula (b1), R¹¹ to R¹⁴ are each independently a primary or secondary alkyl group having 3 to 22 carbon atoms or an alkyl aryl group substituted with an alkyl group having 3 to 18 carbon atoms.

Examples of the primary or secondary alkyl group having 3 to 22 carbon atoms, which may be selected as R¹¹ to R¹⁴, include a primary or secondary propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, a dodecyl group, a tetradecyl group, a hexadecyl group, an octadecyl group, an icosyl group, and an ethylhexyl group.

Examples of the alkyl aryl group substituted with an alkyl group having 3 to 18 carbon atoms, which may be selected as R¹¹ to R¹⁴, include a propylphenyl group, a pentylphenyl group, an octylphenyl group, a nonylphenyl group, and a dodecylphenyl group.

When a compound represented by the above general formula (b1) is used as the ZnDTP (B), one type of the compound may be used alone, or two or more types of the compounds may be used in combination.

Here, in the lubricating oil composition of the one embodiment of the present invention, when the compound represented by the above general formula (b1) is used as the ZnDTP (B), it is preferable to use a primary zinc dialkyl dithiophosphate (primary alkyl ZnDTP) having at least a primary alkyl group, and it is more preferable to use the primary alkyl ZnDTP alone.

When the primary alkyl ZnDTP and a secondary zinc dialkyl dithiophosphate (secondary alkyl ZnDTP) having a secondary alkyl group are used in combination, a content ratio of the primary alkyl ZnDTP to the secondary alkyl ZnDTP [(primary alkyl ZnDTP)/(secondary alkyl ZnDTP)] is, in terms of a mass ratio, preferably 50/50 to 99/1, more preferably 60/40 to 95/5, and still more preferably 70/30 to 90/10.

In the lubricating oil composition of the one embodiment of the present invention, from the viewpoint of being easier to exhibit the effects of the present invention, a content of zinc atoms derived from the ZnDTP (B) is preferably 100 ppm by mass or more, more preferably 110 ppm by mass or more, and still more preferably 120 ppm by mass or more based on the total amount of the lubricating oil composition. In addition, the content of the zinc atoms derived from the ZnDTP (B) is preferably 2,000 ppm by mass or less, more preferably 1,900 ppm by mass or less, and still more preferably 1,800 ppm by mass or less. Upper limit values and lower limit values of these numerical ranges can be freely combined as desired. Specifically, the content of the zinc atoms derived from the ZnDTP (B) is preferably 100 ppm by mass to 2,000 ppm by mass, more preferably 110 ppm by mass to 1,900 ppm by mass, and still more preferably 120 ppm by mass to 1,800 ppm by mass.

In the lubricating oil composition of the one embodiment of the present invention, a content of the ZnDTP (B) may be adjusted so that the content of the zinc atoms derived from the ZnDTP (B) satisfies the above ranges. The content of the ZnDTP (B) is preferably 0.11% by mass or more, more preferably 0.13% by mass or more, and still more preferably 0.14% by mass or more, based on the total amount of the lubricating oil composition. In addition, the content of the ZnDTP (B) is preferably 2.3% by mass or less, more preferably 2.2% by mass or less, and still more preferably 2.1% by mass or less. Upper limit values and lower limit values of these numerical ranges can be freely combined as desired. Specifically, the content of the ZnDTP (B) is preferably 0.11% by mass to 2.3% by mass, more preferably 0.13% by mass to 2.2% by mass, and still more preferably 0.14% by mass to 2.1% by mass.

<Sodium-Based Detergent (C)>

The lubricating oil composition of the present invention contains the sodium-based detergent (C).

When the lubricating oil composition contains the sodium-based detergent (C), the lubricating oil composition is imparted with detergency, and the like.

When the lubricating oil composition does not contain the sodium-based detergent (C), the effects of the present invention by combining the ZnDTP (B) and the sodium-based detergent (C) are not exhibited.

Examples of the sodium-based detergent (C) include sodium salts such as sodium sulfonate, sodium phenate, and sodium salicylate.

Among these, sodium sulfonate is preferred from the viewpoint of being easier to exhibit the effects of the present invention.

Sodium sulfonate is preferably a compound represented by the following general formula (c1).

Sodium phenate is preferably a compound represented by the following general formula (c2).

Sodium salicylate is preferably a compound represented by the following general formula (c3).

One type of the sodium-based detergent (C) may be used alone, or two or more types of the sodium-based detergent (C) may be used in combination.

In the above general formulae (c1) to (c3), R represents a hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms. In the above general formula (c2), q is an integer of 0 or more, and preferably an integer of 0 to 3.

Examples of the hydrocarbon group which may be selected as R include an alkyl group having 1 to 18 carbon atoms, an alkenyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 18 carbon atoms for forming a ring, an aryl group having 6 to 18 carbon atoms for forming a ring, an alkyl aryl group having 7 to 18 carbon atoms, and an aryl alkyl group having 7 to 18 carbon atoms.

The sodium-based detergent (C) may be neutral, basic, or overbased, but is preferably basic or overbased, and more preferably overbased, from a viewpoint of being easier to improve base number retention of the lubricating oil composition.

In this specification, basic or overbased metal-based detergent refers to detergent prepared by causing a metal to react with an acidic organic compound and containing a metal in an amount more than a stoichiometric amount required for neutralization of the metal and the acidic organic compound. That is, when total chemical equivalent of the metal in the metal-based detergent with respect to chemical equivalent of the metal in a metal salt (neutral salt) obtained by the reaction according to the stoichiometric amount required for the neutralization of the metal and the acidic organic compound is defined as a “metal ratio”, the metal ratio of the basic or overbased metal-based detergent becomes larger than 1. The metal ratio of the basic or overbased metal-based detergent used in the present embodiment is preferably more than 1.3, more preferably 5 to 30, and still more preferably 7 to 22.

In this specification, the sodium-based detergent (C) having a base number of less than 50 mgKOH/g measured by a perchloric acid method in conformity with JIS K 2501:2003 is defined as “neutral”, the sodium-based detergent (C) having a base number of 50 mgKOH/g or more and less than 150 mgKOH/g is defined as “basic”, and the sodium-based detergent (C) having a base number of 150 mgKOH/g or more is defined as “overbased”.

The base number of the sodium-based detergent (C) is preferably 5 mgKOH/g or more, more preferably 100 mgKOH/g or more, still more preferably 200 mgKOH/g or more, even more preferably 300 mgKOH/g or more, yet still more preferably 350 mgKOH/g or more, and even still more preferably 400 mgKOH/g or more, and is preferably 600 mgKOH/g or less, more preferably 550 mgKOH/g or less, and still more preferably 500 mgKOH/g or less. Upper limit values and lower limit values of these numerical ranges can be freely combined as desired. Specifically, the base number of the sodium-based detergent (C) is preferably 5 mgKOH/g to 600 mgKOH/g, more preferably 100 mgKOH/g to 550 mgKOH/g, still more preferably 200 mgKOH/g to 500 mgKOH/g, even more preferably 300 mgKOH/g to 500 mgKOH/g, yet still more preferably 350 mgKOH/g to 500 mgKOH/g, and even still more preferably 400 mgKOH/g to 500 mgKOH/g

In the lubricating oil composition of the one embodiment of the present invention, from the viewpoint of being easy to exhibit the effects of the present invention, a content of sodium atoms derived from the sodium-based detergent (C) is preferably 5 ppm by mass or more, more preferably 10 ppm by mass or more, and still more preferably 15 ppm by mass or more, based on the total amount of the lubricating oil composition. In addition, the content of the sodium atoms derived from the sodium-based detergent (C) is preferably 1,000 ppm by mass or less, more preferably 980 ppm by mass or less, and still more preferably 970 ppm by mass or less. Upper limit values and lower limit values of these numerical ranges can be freely combined as desired. Specifically, the content of the sodium atoms derived from the sodium-based detergent (C) is preferably 5 ppm by mass to 1,000 ppm by mass, more preferably 10 ppm by mass to 980 ppm by mass, and still more preferably 15 ppm by mass to 970 ppm by mass.

In the lubricating oil composition of the one embodiment of the present invention, a content of the sodium-based detergent (C) may be adjusted so that the content of the sodium atoms derived from the sodium-based detergent (C) satisfies the above ranges. The content of the sodium-based detergent (C) is preferably 0.01% by mass or more based on the total amount of the lubricating oil composition. In addition, the content of the sodium-based detergent (C) is preferably 0.53% by mass or less, more preferably 0.52% by mass or less, and still more preferably 0.51% by mass or less. Upper limit values and lower limit values of these numerical ranges can be freely combined as desired. Specifically, the content of the sodium-based detergent (C) is preferably 0.01% by mass to 0.53% by mass, more preferably 0.01% by mass to 0.52% by mass, and still more preferably 0.01% by mass to 0.51% by mass.

<Other Additives>

The lubricating oil composition of the one embodiment of the present invention may contain additives for lubricating oil other than the component (B) and the component (C) as long as the effects of the present invention are not impaired.

Examples of the additives for lubricating oil include an antioxidant, a viscosity index improver, a pour-point depressant, a rust inhibitor, a metal deactivator, an anti-foaming agent, an extreme pressure agent, an anti-wear agent, an oiliness agent, and metal-based detergent (C′) other than the sodium-based detergent (C).

One type of these additives for lubricating oil may be used alone, or two or more types of these additives for lubricating oil may be used in combination.

In this specification, in consideration of handling properties and solubility in the base oil (A), the additive such as the viscosity index improver and the anti-foaming agent may be in a form of a solution obtained by diluting the additive with and a part of the base oil (A) described above to cause the additive to be dissolved therein. In such a case, in this specification, a content, which will be described later, of the additive, such as the anti-foaming agent and the viscosity index improver, means a content as expressed in terms of an effective component excluding a diluent oil (expressed in terms of a resin content).

(Antioxidant)

Examples of the antioxidant include an amine-based antioxidant and a phenol-based antioxidant. One type of these antioxidants may be used alone, or two or more types of these antioxidants may be used in combination.

Examples of the amine-based antioxidant include: monoalkyl diphenylamine-based compounds such as monooctyl diphenylamine and mono nonyl diphenylamine; dialkyl diphenylamine-based compounds such as 4,4′-dibutyldiphenylamine, 4,4′-dipentyldiphenylamine, 4,4′-dihexyldiphenylamine, 4,4′-diheptyldiphenylamine, 4,4′-dioctyldiphenylamine, 4,4′-dinonyldiphenylamine, and monobutylphenylmonooctylphenylamine; polyalkyl diphenylamine-based compounds such as tetrabutyldiphenylamine, tetrahexyldiphenylamine, tetraoctyldiphenylamine, and tetranonyldiphenylamine; and naphthylamine-based compounds such as α-naphthylamine, phenyl-α-naphthylamine, butylphenyl-α-naphthylamine, pentylphenyl-α-naphthylamine, hexylphenyl-α-naphthylamine, heptylphenyl-α-naphthylamine, octylphenyl-α-naphthylamine, and nonylphenyl-α-naphthylamine.

Examples of the phenol-based antioxidant include: monophenol-based compounds, such as 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, and octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; and diphenol-based compounds such as 4,4′-methylenebis(2,6-di-tert-butylphenol) and 2,2′-methylenebis(4-ethyl-6-tert-butylphenol).

When the lubricating oil composition of the one aspect of the present invention contains an antioxidant, a content of the antioxidant may be a minimum amount required for maintaining the oxidation stability, and is preferably 0.01% by mass to 1.5% by mass, and more preferably 0.1% by mass to 1% by mass, based on the total amount of the lubricating oil composition.

(Viscosity Index Improver)

Examples of the viscosity index improver include polymers, such as a non-dispersant-type polymethacrylate, a dispersant-type polymethacrylate, an olefin-based copolymer (for example, an ethylene-propylene copolymer), a dispersant-type olefin-based copolymer, and a styrene-based copolymer (for example, a styrene-diene copolymer and a styrene-isoprene copolymer). One type of these viscosity index improvers may be used alone, or two or more types of these viscosity index improvers may be used in combination.

When the lubricating oil composition of the one aspect of the present invention contains a viscosity index improver, a content of the viscosity index improver as expressed in terms of a resin content is preferably 0.01% by mass to 10% by mass, more preferably 0.02% by mass to 7% by mass, and still more preferably 0.03% by mass to 5% by mass, based on the total amount of the lubricating oil composition.

(Pour-Point Depressant)

Examples of the pour-point depressant include polymethacrylate having a mass average molecular weight of about 50,000 to 150,000. One type of these pour-point depressants may be used alone, or two or more types of these pour-point depressants may be used in combination.

When the lubricating oil composition of the one aspect of the present invention contains a pour-point depressant, a content of the pour-point depressant is preferably 0.01% by mass to 5% by mass, and more preferably 0.02% by mass to 2% by mass, based on the total amount of the lubricating oil composition.

(Rust Inhibitor)

Examples of the rust inhibitor include alkylbenzene sulfonate, dinonyl naphthalene sulfonate, an organic phosphite ester, an organic phosphate ester, an alkenyl succinate, and an ester of an alkenyl succinic acid and a polyhydric alcohol. One type of these rust inhibitors may be used alone, or two or more types of these rust inhibitors may be used in combination.

When the lubricating oil composition of the one aspect of the present invention contains a rust inhibitor, a content of the rust inhibitor is preferably 0.01% by mass to 10.0% by mass, and more preferably 0.03% by mass to 5.0% by mass, based on the total amount of the lubricating oil composition.

(Metal Deactivator)

Examples of the metal deactivator include benzotriazole-based compounds, tolyltriazole-based compounds, thiadiazole-based compounds, imidazole-based compounds, and pyrimidine-based compounds. One type of these metal deactivators may be used alone, or two or more types of these metal deactivators may be used in combination.

When the lubricating oil composition of the one aspect of the present invention contains a metal deactivator, a content of the metal deactivator is preferably 0.01% by mass to 5.0% by mass, and more preferably 0.03% by mass to 3.0% by mass, based on the total amount of the lubricating oil composition.

(Anti-Foaming Agent)

Examples of the anti-foaming agent include silicone-based anti-foaming agents, fluorine-based anti-foaming agents such as fluorosilicone oils and fluoroalkyl ethers, and polyacrylate-based anti-foaming agents. One type of these metal deactivators may be used alone, or two or more types of these metal deactivators may be used in combination.

When the lubricating oil composition of the one aspect of the present invention contains an anti-foaming agent, a content of the anti-foaming agent as expressed in terms of a resin content is preferably 0.0001% by mass to 0.20% by mass, and more preferably 0.0005% by mass to 0.10% by mass, based on the total amount of the lubricating oil composition.

(Extreme Pressure Agent or Anti-Wear Agent)

The lubricating oil composition of the one aspect of the present invention may contain one or more selected from a group consisting of an extreme pressure agent and an anti-wear agent, but from the viewpoint of being easy to exhibit the effects of the present invention, a content of the one or more selected from the group consisting of the extreme pressure agent and the anti-wear agent is preferably small.

Examples of the extreme pressure agent and the anti-wear agent include organic metal-based compounds, sulfur-based compounds, phosphorus-based compounds, and sulfur-phosphorus-based compounds, which do not correspond to the component (B).

Examples of the organic metal-based compounds include organic molybdenum-based compounds such as molybdenum dialkyl dithiocarbamate (MoDTC) and molybdenum dialkyl dithiophosphate (MoDTP), and organic zinc-based compounds other than the component (B) such as zinc dialkyl dithiocarbamate (ZnDTC).

Examples of the sulfur-based compounds include sulfurized fats and oils, sulfurized fatty acids, sulfurized esters, sulfurized olefins, monosulfides, polysulfides, dihydrocarbyl sulfides, thiadiazole compounds, alkylthiocarbamoyl compounds, thiocarbamate compounds, thioterpene compounds, and dialkyl thiodipropionate compounds.

Examples of the phosphorus-based compound include: phosphate esters such as an aryl phosphate, an alkyl phosphate, an alkenyl phosphate, and an alkyl aryl phosphate; phosphite esters such as an aryl hydrogen phosphite, an alkyl hydrogen phosphite, an aryl phosphite, an alkyl phosphite, an alkenyl phosphite, and an aryl alkyl phosphite; and amine salts thereof.

Examples of the sulfur-phosphorus-based compounds include a monoalkyl thiophosphate, a dialkyl dithiophosphate, a trialkyl trithiophosphate, and amine salts thereof.

In the lubricating oil composition of the one aspect of the present invention, the content of the one or more selected from the group consisting of the extreme pressure agent and the anti-wear agent is usually about 0.05% by mass to 10% by mass, and preferably 0.1% by mass to 5% by mass, based on the total amount of the lubricating oil composition.

However, from the viewpoint of ensuring the oxidation stability, preventing sludge formation, preventing the color deterioration, and the like, among the phosphorus-based compounds, it is preferable to contain, in a small amount, the following compounds: acidic phosphate esters such as monoaryl acidphosphate, diaryl acid phosphate, monoalkyl acid phosphate, dialkyl acidphosphate, monoalkenyl acid phosphate, and dialkenyl acid phosphate; acidic phosphite esters such as monoalkyl acid phosphite, dialkyl acid phosphite, monoalkenyl acid phosphite, and dialkenyl acid phosphite; and amine salts thereof. Specifically, based on the total amount of the lubricating oil composition, a content of these phosphorus-based compounds is preferably less than 0.01% by mass, more preferably less than 0.001% by mass, and it is even more preferable that the lubricating oil composition does not contain any of these phosphorus-based compounds.

(Oiliness Agent)

Examples of the oiliness agent include aliphatic alcohols; fatty acid compounds such as fatty acids and fatty acid metal salts; ester compounds such as polyol esters, sorbitan esters, and glycerides; and amine compounds such as aliphatic amines.

From a viewpoint of addition effects, a content of the oiliness agent is usually 0.1% by mass to 10% by mass, and preferably 0.5% by mass to 5% by mass, based on the total amount of the lubricating oil composition.

<Metal-Based Detergent (C′) Other Than Sodium-Based Detergent (C)>

The lubricating oil composition of the one embodiment of the present invention may contain a metal-based detergent (C′) other than the sodium-based detergent (C), but from the viewpoint of being easier to exhibit the effects of the present invention, a content of the metal-based detergent (C′) other than the sodium-based detergent (C) is preferably small.

Examples of the metal-based detergent (C′) other than the sodium-based detergent (C) include magnesium-based detergent and calcium-based detergent.

Examples of the magnesium-based detergent include magnesium salts such as magnesium sulfonate, magnesium phenate, and magnesium salicylate. The magnesium-based detergent may be neutral, basic, or overbased.

Examples of the calcium-based detergent include calcium salts such as calcium sulfonate, calcium phenate, and calcium salicylate. The calcium-based detergent may be neutral, basic, or overbased.

In the lubricating oil composition of the one embodiment of the present invention, a content of metal atoms derived from the metal-based detergent (C′) other than the sodium-based detergent (C) is preferably small. In the lubricating oil composition, a content of magnesium atoms derived from the magnesium-based detergent is preferably less than 30 ppm by mass, more preferably less than 20 ppm by mass, still more preferably less than 10 ppm by mass, even more preferably less than 1 ppm by mass, and it is yet still more preferable that the lubricating oil composition does not contain the magnesium atoms derived from the magnesium-based detergent, based on the total amount of the lubricating oil composition.

In the lubricating oil composition of the one embodiment of the present invention, the content of the magnesium atoms derived from the magnesium-based detergent is preferably small. In the lubricating oil composition, the content of the magnesium atoms derived from the magnesium-based detergent is preferably less than 30 ppm by mass, more preferably less than 20 ppm by mass, still more preferably less than 10 ppm by mass, even more preferably less than 1 ppm by mass, and it is yet still more preferable that the lubricating oil composition does not contain the magnesium atoms derived from the magnesium-based detergent, based on the total amount of the lubricating oil composition.

In the lubricating oil composition of the one embodiment of the present invention, a content of calcium atoms derived from the calcium-based detergent is preferably small. In the lubricating oil composition, the content of the calcium atoms derived from the calcium-based detergent is preferably less than 30 ppm by mass, more preferably less than 20 ppm by mass, still more preferably less than 10 ppm by mass, even more preferably less than 1 ppm by mass, and it is yet still more preferable that the lubricating oil composition does not contain the calcium atoms derived from the calcium-based detergent, based on the total amount of the lubricating oil composition.

[Physical Properties of Lubricating Oil Composition] <Kinematic Viscosity at 40° C., Viscosity Index>

A kinematic viscosity at 40° C. of the lubricating oil composition of the one embodiment of the present invention is preferably 9.00 mm²/s to 165 mm²/s, more preferably 20.0 mm²/s to 120 mm²/s, and still more preferably 25.0 mm²/s to 100 mm²/s.

When the kinematic viscosity at 40° C. of the lubricating oil composition is 9.00 mm²/s or more, the lubricating oil composition having a high flash point and excellent lubricating performance can be easily obtained. In addition, when the kinematic viscosity at 40° C. of the base oil (A) is 165 mm²/s or less, viscosity resistance at a low temperature is not excessively large, so that operations of a machine are easily improved.

In addition, a viscosity index of the lubricating oil composition of the one embodiment of the present invention is preferably 80 or more, more preferably 90 or more, and still more preferably 100 or more.

The kinematic viscosity at 40° C. and the viscosity index mean values measured or calculated in conformity with JIS K 2283:2000.

<Content of Zinc Atoms>

In the lubricating oil composition of the present invention, the content of the zinc atoms is 100 ppm by mass to 2,000 ppm by mass, based on the total amount of the lubricating oil composition.

When the content of the zinc atoms is less than 100 ppm by mass, the anti-oxidation ability, the anti-wear ability, and the effects of the present invention are hardly exhibited. When the content of the zinc atoms is more than 2,000 ppm by mass, the effects of the present invention are hardly exhibited.

Here, from the viewpoint of being easier to exhibit the effects of the present invention, and from a viewpoint of preparing a lubricating oil composition having excellent an anti-oxidation ability and an anti-wear ability, the content of the zinc atoms of the lubricating oil composition of the one aspect of the present invention is preferably 110 ppm by mass or more, and more preferably 120 ppm by mass or more, based on the total amount of the lubricating oil composition. In addition, the content of the zinc atoms is preferably 1,900 ppm by mass or less, and more preferably 1,800 ppm by mass or less. Upper limit values and lower limit values of these numerical ranges can be freely combined as desired. Specifically, the content of the zinc atoms of the lubricating oil composition of the one embodiment of the present invention is preferably 110 ppm by mass to 1,900 ppm by mass, and more preferably 120 ppm by mass to 1,800 ppm by mass. In this specification, the content of the zinc atoms of the lubricating oil composition means a value measured in conformity with the ASTM D4951.

<Content of Sodium Atoms>

In the lubricating oil composition of the present invention, the content of the sodium atoms is 5 ppm by mass to 1,000 ppm by mass based on the total amount of the lubricating oil composition.

When the content of the sodium atoms is less than 5 ppm by mass, a lubricating oil composition having poor detergency is obtained, and the effects of the present invention are hardly exhibited. When the content of the sodium atoms is more than 1,000 ppm by mass, the effects of the present invention are hardly exhibited.

Here, from the viewpoint of being easier to exhibit the effects of the present invention, and from a viewpoint of preparing a lubricating oil composition having excellent detergency, the content of the sodium atoms of the lubricating oil composition of the one aspect of the present invention is preferably 10 ppm by mass or more, and more preferably 15 ppm by mass or more, based on the total amount of the lubricating oil composition. In addition, the content of the sodium atoms of the lubricating oil composition of the one aspect of the present invention is preferably 980 ppm by mass or less, and more preferably 970 ppm by mass or less. Upper limit values and lower limit values of these numerical ranges can be freely combined as desired. Specifically, the content of the sodium atoms of the lubricating oil composition of the one aspect of the present invention is preferably 10 ppm by mass to 980 ppm by mass, and more preferably 15 ppm by mass to 970 ppm by mass.

In this specification, the content of the sodium atoms of the lubricating oil composition means a value measured in conformity with the ASTM D4951.

<Content Ratio of Content of Zinc Atoms to Content of Sodium Atoms>

In the lubricating oil composition of the one embodiment of the present invention, from the viewpoint of being easier to exhibit the effects of the present invention, a content ratio [(Zn)/(Na)] of the content of the zinc atoms to the content of the sodium atoms is, in terms of a mass ratio, preferably 0.050 or more, more preferably 0.080 or more, and still more preferably 0.10 or more. In addition, the content ratio [(Zn)/(Na)] of the content of the zinc atoms to the content of the sodium atoms is preferably 50 or less, more preferably 30 or less, and still more preferably 20 or less. Upper limit values and lower limit values of these numerical ranges can be freely combined as desired. Specifically, the content ratio [(Zn)/(Na)] of the content of the zinc atoms to the content of the sodium atoms is preferably 0.050 to 50, more preferably 0.080 to 30, and still more preferably 0.10 to 20.

<Content of Magnesium Atoms>

In the lubricating oil composition of the one embodiment of the present invention, from the viewpoint of being easier to exhibit the effects of the present invention, the content of the magnesium atoms is preferably less than 30 ppm by mass, more preferably less than 20 ppm by mass, still more preferably less than 10 ppm by mass, even more preferably less than 1 ppm by mass, and it is yet still more preferable that the lubricating oil composition does not contain the magnesium atoms, based on the total amount of the lubricating oil composition.

In this specification, the content of the magnesium atoms of the lubricating oil composition means a value measured in conformity with the ASTM D4951.

<Content of Calcium Atoms>

In the lubricating oil composition of the one embodiment of the present invention, from the viewpoint of being easier to exhibit the effects of the present invention, the content of the calcium atoms is preferably less than 30 ppm by mass, more preferably less than 20 ppm by mass, still more preferably less than 10 ppm by mass, even more preferably less than 1 ppm by mass, and it is yet still more preferable that the lubricating oil composition does not contain the calcium atoms, based on the total amount of the lubricating oil composition.

In this specification, the content of the calcium atoms of the lubricating oil composition means a value measured in conformity with the ASTM D4951.

<ASTM Color after ISOT Test>

For the lubricating oil composition of the one embodiment of the present invention, an ASTM color after a copper piece and an iron piece are put as catalysts and an ISOT test in conformity with JIS K2514-1:2013 is performed at 150° C. for 168 hours is preferably 1.0 or less, and more preferably 0.5 or less.

[Method for Producing Lubricating Oil Composition]

A method for producing the lubricating oil composition of the present invention is not particularly limited.

For example, the method for producing the lubricating oil composition of the one aspect of the present invention is a method for producing a lubricating oil composition, including a step of mixing the base oil (A), the ZnDTP (B), and the sodium-based detergent (C).

A method of mixing the above components is not particularly limited, and examples thereof include a method including a step of blending the component (B) and the component (C) with the base oil (A). The component (B) and the component (C) may be blended with the base oil (A) at the same time, or may be blended separately. The same applies to components other than the component (B) and the component (C). In addition, each of the components may be blended after being converted into a form of a solution (dispersion) upon addition with a diluent oil or the like. It is preferred that after blending the respective components, the blend is stirred and uniformly dispersed by a known method.

[Application of Lubricating Oil Composition]

The lubricating oil composition of the present invention has alleviated color deterioration over time, and therefore can be suitably used for machines, facilities, and the like that employ a technique of visually checking a state of contamination, a state of generation of precipitates, and the like. The lubricating oil composition also has excellent oxidation stability.

Therefore, the lubricating oil composition can be suitably used as a hydraulic oil, a compressor oil, a gear oil, a cutting oil, a machine tool oil, a refrigerator oil, a turbine oil, an internal combustion machine oil, a transmission oil, and the like, and can be particularly suitably used as the hydraulic oil.

Therefore, in the one aspect of the present invention, the following method is provided.

(1) A method for using the lubricating oil composition of the present invention as a hydraulic oil, a compressor oil, a gear oil, a cutting oil, a machine tool oil, a refrigerator oil, a turbine oil, an internal combustion machine oil, or a transmission oil.

(2) A method for using the lubricating oil composition of the present invention as a hydraulic oil.

[One Aspect of Present Invention to be Provided]

In the one embodiment of the present invention, the following [1] to [6] are provided.

[1] A lubricating oil composition containing:

a base oil (A);

a zinc dialkyl dithiophosphate (B); and

a sodium-based detergent (C),

wherein a content of zinc atoms is 100 ppm by mass to 2,000 ppm by mass based on a total amount of the lubricating oil composition, and

a content of sodium atoms is 5 ppm by mass to 1,000 ppm by mass based on the total amount of the lubricating oil composition.

[2] The lubricating oil composition according to [1], wherein a content ratio [(Zn)/(Na)] of the zinc atoms (Zn) in the lubricating oil composition to the sodium atoms (Na) in the lubricating oil composition is 0.050 to 50 in terms of a mass ratio. [3] The lubricating oil composition described in [1] or [2], wherein a content of magnesium atoms is less than 30 ppm by mass based on the total amount of the lubricating oil composition. [4] The lubricating oil composition according to any one of [1] to [3], wherein a content of calcium atoms is less than 30 ppm by mass based on the total amount of the lubricating oil composition. [5] The lubricating oil composition according to any one of [1] to [4], wherein an ASTM color after a copper piece and an iron piece are put as catalysts and an ISOT test in conformity with JIS K2514-1:2013 is performed at 150° C. for 168 hours is 1.0 or less. [6] The lubricating oil composition according to any one of [1] to [5], wherein the base oil (A) has a kinematic viscosity at 40° C. of 9.00 mm²/s to 165 mm²/s.

EXAMPLES

The present invention will be described in detail with reference to the following Examples, but the present invention is not limited to the following Examples.

[Method for Measuring Various Physical Properties]

Physical property values of the base oil and the lubricating oil composition used in each of Examples and Comparative Examples were measured according to the following procedures.

(1) Kinematic Viscosity and Viscosity Index

The kinematic viscosity at 40° C. and the viscosity index were measured and calculated in conformity with JIS K2283:2000.

(2) Sodium Atom Amount and Zinc Atom Amount

A calcium atom amount, a magnesium atom amount, a sodium atom amount, and a zinc atom amount of the lubricating oil composition were measured in conformity with the ASTM D4951.

Examples 1 to 11 and Comparative Examples 1 to 7

Base oils and various additives shown below were thoroughly mixed in blending amounts (% by mass) shown in Table 1 to prepare lubricating oil compositions, respectively.

Details of the base oils and various additives used in the Examples 1 to 11 and Comparative Examples 1 to 7 are as follows.

<Base Oil (A)>

Mineral oils classified into Group II under the API category (kinematic viscosity at 40° C.=30.6 mm²/s, viscosity index=104) were used.

<Zinc Dialkyl Dithiophosphate (B)>

In the above general formula (b1), the primary zinc dialkyl dithiophosphate in which R¹¹ to R¹⁴ are 2-ethylhexyl groups (primary alkyl groups) was used.

Content of zinc atoms: 8.90% by mass, content of phosphorus atoms: 7.40% by mass, content of sulfur atoms: 15.0% by mass

In Table 1, the zinc dialkyl dithiophosphate (B) is abbreviated as “ZnDTP”.

<Sodium-Based Detergent (C), Metal-Based Detergent (C′) Other Than Sodium-Based Detergent>

Na sulfonate (base number: 448 mgKOH/g, content of sodium atoms: 19.5% by mass)

Ca sulfonate (base number: 307 mgKOH/g, content of calcium atoms: 11.9% by mass)

Mg sulfonate (base number: 308 mgKOH/g, content of magnesium atoms: 9.4% by mass)

The base numbers of the sodium-based detergent (C) and the metal-based detergent (C′) other than the sodium-based detergent were measured by the perchloric acid method in conformity with JIS K2501-9:2003.

[Evaluation] <ISOT Test>

A copper piece and an iron piece were put into a test oil (lubricating oil composition) as catalysts, and an ISOT test in conformity with JIS K2514-1:2013 was performed to forcibly deteriorate the test oil. A test temperature was set to 150° C., and an ASTM color (JIS K2580:2003) was measured for the test oil before a start of the ISOT test, after 72 hours from the start of the ISOT test, and after 168 hours from the start of the ISOT test.

Then, a sample oil having an ASTM color of 1.0 or less (L1.0) was determined as “no color deterioration”, and a sample oil having an ASTM color of more than 1.0 (L1.5, L2.0, and the like) was determined as “having color deterioration”.

<Base Number>

A base number (B_(0h)) of the test oil before the start of the ISOT test, a base number (B_(72h)) of the test oil after 72 hours from the start of the ISOT test, and a base number (B_(168h)) of the test oil after 168 hours from the start of the ISOT test were measured by a hydrochloric acid method in conformity with JIS K2501-8:2003.

Then, a “base number retention S_(72h)(%) after 72 hours from the start of the ISOT test” and a “base number retention S_(168h)(%) after 168 hours from the start of the ISOT test” were calculated by the following equations.

S _(72h)(%)={(B _(72h))/(B _(0h))}×100

S _(168h)(%)={B _(168h)/(B _(0h))}×100

Results are shown in Table 1.

TABLE 1 Examples 1 2 3 4 5 6 7 8 9 Composition Base oil (A) 99.7 99.67 99.47 99.84 99.69 98.99 98.75 97.50 99.80 (unit: % by ZnDTP 0.28 0.28 0.28 0.15 0.30 1.00 1.00 2.00 0.15 mass) Ca sulfonate — — — — — — — — — Mg sulfonate — — — — — — — — — Na sulfonate 0.02 0.05 0.25 0.01 0.01 0.01 0.25 0.50 0.50 Various atom Ca amount — — — — — — — — — amounts in (ppm by mass) hydraulic oil Mg amount — — — — — — — — — composition, (ppm by mass) and the like Na amount 33 92 532 20 20 19 467 928 942 (ppm by mass) Zn amount 255 259 249 132 267 869 887 1750 126 (ppm by mass) Zn/Na 7.7 2.8 0.5 6.6 13.4 45.7 1.9 1.9 0.13 Evaluation 1 Color (ASTM) L0.5 L0.5 L0.5 L0.5 L0.5 L0.5 L0.5 L0.5 L0.5 Before start Base number 0.19 0.31 1.28 0.17 0.19 0.26 1.38 2.56 2.43 of ISOT test (mgKOH/g) Evaluation2 Color (ASTM) L0.5 L0.5 L0.5 L0.5 L0.5 L0.5 L0.5 L0.5 L0.5 After 72 hours Base number 0.18 0.30 1.25 0.15 0.17 0.21 1.15 2.12 2.33 from start of (mgKOH/g) ISOT test Base number 94.7 96.8 97.7 88.2 89.5 80.8 83.3 82.8 95.9 retention (%) Evaluation3 Color (ASTM) L0.5 L0.5 L0.5 L0.5 L0.5 L1.0 L0.5 L0.5 L0.5 After 168 hours Base number 0.18 0.29 1.20 0.14 0.16 0.22 1.07 1.68 2.29 from start of (hydrochloric ISOT test acid method) Base number 94.7 93.5 93.8 82.4 84.2 84.6 77.5 65.6 94.2 retention (%) Examples Comparative Examples 10 11 1 2 3 4 5 6 7 Composition Base oil (A) 99.00 98.50 99.72 98.98 99.98 99.83 99.69 99.63 99.68 (unit: % by ZnDTP 0.50 1.00 0.28 1.00 — — 0.28 0.28 0.28 mass) Ca sulfonate — — — — — — 0.03 0.09 — Mg sulfonate — — — — — — — — 0.04 Na sulfonate 0.50 0.50 — — 0.02 0.50 — — — Various atom Ca amount — — — — — — 36 105 — amounts in (ppm by mass) hydraulic oil Mg amount — — — — — — — — 40 composition, (ppm by mass) and the like Na amount 958 878 — — 42 956 — — — (ppm by mass) Zn amount 454 851 253 879 — — 248 249 255 (ppm by mass) Zn/Na 0.5 1.0 — — — — — — — Evaluation 1 Color (ASTM) L0.5 L0.5 L0.5 L0.5 L0.5 L0.5 L0.5 L0.5 L0.5 Before start Base number 2.53 2.45 0.08 0.14 0.12 2.41 0.14 0.33 0.20 of ISOT test (mgKOH/g) Evaluation2 Color (ASTM) L0.5 L0.5 L2.0 L6.0 L7.5 D8.0 L1.5 L1.5 L2.0 After 72 hours Base number 2.36 2.33 0.08 0.11 0.08 0.33 0.11 0.22 0.16 from start of (mgKOH/g) ISOT test Base number 93.3 95.1 100.0 78.6 66.7 13.7 78.6 66.7 80.0 retention (%) Evaluation3 Color (ASTM) L0.5 L0.5 L4.0 L8.0 D8.0 D8.0 L3.5 L3.0 L3.0 After 168 hours Base number 2.26 2.29 0.07 0.08 0.05 0.30 0.06 0.13 0.08 from start of (hydrochloric ISOT test acid method) Base number 89.3 93.5 87.5 57.1 41.7 12.4 42.9 39.4 40.0 retention (%)

The following can be seen from Table 1.

In the lubricating oil compositions of Examples 1 to 11, no color deterioration was observed even after 168 hours from the start of the ISOT test.

In contrast, in Comparative Examples 1 and 2 in which the ZnDTP was blended and Na sulfonate was not blended, the color deterioration was observed after 72 hours from the start of the ISOT test.

In addition, in Comparative Examples 3 and 4 in which Na sulfonate was blended and the ZnDTP was not blended, the color deterioration was observed after 72 hours from the start of the ISOT test.

Further, in Comparative Examples 5 and 6 in which Ca sulfonate was blended instead of Na sulfonate, and in Comparative Example 7 in which Mg sulfonate was blended instead of Na sulfonate, the color deterioration was observed after 72 hours from the start of the ISOT test. 

1. A lubricating oil composition, comprising: a base oil (A); a zinc dialkyl dithiophosphate (B); and a sodium-based detergent (C), wherein a content of zinc atoms is 100 ppm by mass to 2,000 ppm by mass based on a total amount of the lubricating oil composition, and wherein a content of sodium atoms is 5 ppm by mass to 1,000 ppm by mass based on the total amount of the lubricating oil composition.
 2. The composition of claim 1, wherein a content ratio [(Zn)/(Na)] of the zinc atoms (Zn) in the lubricating oil composition to the sodium atoms (Na) in the lubricating oil composition is 0.050 to 50 in terms of a mass ratio.
 3. The composition of claim 1, wherein a content of magnesium atoms is less than 30 ppm by mass based on the total amount of the composition.
 4. The composition of claim 1, wherein a content of calcium atoms is less than 30 ppm by mass based on the total amount of the composition.
 5. The composition of claim 1, wherein an ASTM color after a copper piece and an iron piece are put as catalysts and an ISOT test in conformity with JIS K2514-1:2013 is performed at 150° C. for 168 hours is 1.0 or less.
 6. The composition of claim 1, wherein the base oil (A) has a kinematic viscosity at 40° C. of 9.00 mm²/s to 165 mm²/s. 